Patent GB-600252-A (GB)
Title: Synchronising arrangements for multiplex electric pulse communication systems
IPC: H04J3/04
Filed: 1944-10-06
Abstract: 600,252. Thermionic distributers. STANDARD TELEPHONES & CABLES, Ltd. Oct. 6, 1944, No. 19192. Convention date, Dec. 20, 1943. [Class 40 (iii)] [Also in Group XL (c)] In a multiplex pulse communication system, a synchronizing signal is superimposed on one of the signal channels. Separating means, provided at the receiving terminal for each channel, are controlled by an oscillator of free frequency rather less than the repetition frequency of one channel. The synchronizing signal is selected from the output of one channel by a filter and is applied to maintain in synchronism the controlling oscillator. Signals from the lines 10 &c., Fig. 1, pass via hybrid coils 14 to channel modulators 18 operated in sequence by pulses derived from the source 23 over phase-adjusters 24. One modulator 18 is also supplied with synchronizing signals from the source 22. In the receiver the interlaced channels are separated by selectors 34, demodulated signals from the detectors 30 passing to the lines 52 via hybrid coils 48. The detector 30 in one channel is provided with a filter 42 which passes the synchronizing signal to lock the generator 38. Pulses from the generator 38, which may be a multivibrator, are applied over delay networks 39 to operate the channel selectors 34. Pulses are also applied to control the wave generator 43 supplying demodulating signals to the detectors 30 via phase-shifters 44. A stop filter 56 prevents synchronizing signals from reaching the line 52. In an alternative arrangement, in which the detectors 30 include individual demodulating means, the source 43 and phaseshifters 44 may be omitted. Channel modulator for pulse time-modulated waves (Fig. 2). Signals from the line 60 pass to the grid of the valve 71 via the synchronizing frequency stop filter 61. A synchronizing signal is applied to the valve 72 from the line 62, combined signals appearing in the coils 76 of the modulating transformer. Control waves are applied to the coil 78, the modulated waves appearing in the coils 80, 81 being applied to the rectifiers 82, 83. The output from the valves 82, 83 is combined, and passed over the shaping circuit 89 to the line. In the channels not carrying superimposed synchronizing signals the valve 72 may be omitted. Specification 600,244, [Group XL (c)], is referred to. Channel selector (Fig. 3) (34 of Fig. 1). Signals from'the line 28 are applied to the overbiassed valve 100. Gating pulses from the generator 38 are applied to unblock the valve 100, the amplitude being determined by the limiter 105. Pulse time modulation detector. Pulses of the selected channel are applied to a grid of the valve 110, Fig. 3, a second grid being supplied with A.C. of a frequency which is a harmonic of that of the control wave. The detected signal passes to the hybrid coil 48, Fig. 1, over the pulse-frequency stop filter 111 and synchronizing frequency stop filter 56, synchronizing signals appearing on the line 112. In an alternative arrangement (Fig. 4, not shown), the second grid of the valve 110 is grounded through a tuned circuit in which the detecting wave is generated from the signal impulses. Specifications 520,448 and 600,291, [Group XL (c)], also are referred to. In a modified form of the invention, a receiving channel is caused to pick out any desired transmission channel, each receiving channel possessing its own selector wave generator and the desired transmission channel being modulated with the appropriate synchronizing signal. The invention may also be employed for the interception of any desired channel at an intermediate point in the line 28.